Mullion for a window



FIG. 1 is a top perspective view of a mullion for a window showing my new design;

FIG. 2 is a left side view thereof, the right side view being a mirror image;

FIG. 3 is an enlarged front view thereof, the rear view being a mirror image thereof; and,

FIG. 4 is a top view thereof, the bottom view being a mirror image.

The broken lines illustrate portions of the mullion for a window that form no part of the claimed design.

The mullion for a window is shown with a symbolic break in its length. The appearance of any portion of the mullion for a window between the break lines forms no part of the claimed design. 

CLAIM The ornamental design for a mullion for a window, as shown and described. 